The present invention relates to printing methods in general, and in particular to methods for compensating for dot gain without decreasing tonal range or losing detail.
One of the most common artifacts that occurs in printing is dot gain. Dot gain occurs when the size of an ink dot that is printed on a media such as paper, fabric, aluminum, plastic, etc. is larger than desired. Dot gain can occur due to the compression of ink as it is pressed onto the media as well as by the spreading of the ink when absorbed by certain media such as news print, etc. In addition, dot gain can occur as a result of flaws in output devices using the printing process.
Because smaller dots are affected by dot gain more than larger dots, the artifact is particularly noticeable in stochastic screening whereby all the dots that comprise the images are the same size and relatively small. In the past, most methods of compensating for dot gain involved the redistribution and/or removal of a number of dots that are printed. However, the redistribution and/or removal of dots generally reduces the number of dots per unit area, thereby causing a corresponding loss of detail and diminishing the tonal range in there resulting image.
Given the problems associated with dot gain in stochastic printing, there is a need for a mechanism that can compensate for dot gain without removing detail and/or tonal range from an image.
To address the problems caused by dot gain in printing that utilizes stochastic screens, the present invention comprises a method of creating stochastic screens wherein the size of the individual dots in the screens are modified to compensate for dot gain that occurs during the printing process.
Continuous tone cyan, magenta, yellow and black (CMYK) images are received at a first resolution. A CMYK continuous tone image is applied to a screening program that creates stochastic CMYK files at the first resolution. The CMYK files are then expanded to the resolution of an output device that will print the image. As a result of the integer expansion, each dot in the original stochastic screen file will be represented as multiple subdots in the expanded stochastic screen file. One or more of the multiple subdots that correspond to each dot in the original stochastic screen file are removed to compensate for dot gain that occurs when the expanded stochastically screened images are printed. In addition, the removal of some of the subdots aids linearization by improving the tonal range.
According to another embodiment of the invention, the system determines when dots in the original stochastic screen files overlap to create a particular color. These dots are then removed from the original stochastically screened files and additional screen files are added that print dots with the color and the location of the previously overlapping dots.